Exploration and production of hydrocarbons from subsea wells require various and complex equipment, such as wellhead equipment, tie-in stations, compressors and pipelines. This subsea equipment is in frequent need of maintenance, emergency repairs, and upgrade operations. In order to perform these operations, offshore workers need various tools, spare parts, etc. Offshore units, such as floating platforms, subsea vessels and anchor-handling vessels, are in general lacking in storage space, so tools and parts are normally stored onshore until they are needed offshore.
Consequently, it is necessary to be able to quickly transfer articles from land to the offshore units. As soon as the requirement for a specific article emerges at an offshore site, a request is made to an onshore supply operation. The article is then collected from the storage area and transferred by e.g. supply boats to the offshore unit, but supply boats are costly to operate and dependent on the weather. Alternatively, the subsea vessel can abort its current mission and collect articles from the onshore location, but this is also a costly and undesirable operation.
Depending on the weather, the supply boats may not be capable of handing over the articles to the offshore unit within the requested time. The timing of delivering the articles is critical, and delayed delivery of maintenance equipment to the offshore unit can be both critical and costly. It is also the case that at some onshore locations, the logistics is difficult and slow. In worst case scenarios equipment for maintaining the safety of the offshore workers will not reach the offshore unit in time.
Attempts have been made to overcome the problem of lack of offshore storage space. Examples include containers for storing articles on site, where the containers are buoyant and floating in the water. The floating containers are anchored to the seabed, making them unsuitable for extended storage due to exposure to wind, waves and currents, and adding the risk of the containers becoming detached from the anchor and colliding with offshore installations or vessels.